Are you selecting a safety relay just to meet the SIL3 requirements?
Who will be responsible for conducting the Proof Test to ensure it is still safety relays are still safe to use?
Which is critical? Safety relays without diagnostics or the Safety relays with diagnostics?
Safety is a Choice, Not by Chance
The graphics below explains the functional principle of the force guided /positive driven contacts in the event of a welded contacts and that’s where the normally closed contacts come into action to provide feedback to inform the system of the failure in relay contacts.
In this case when the relay is de-energized, the normally closed contact cannot close properly having a gap of 0.5mm.
Safety relays for ESD-Emergency Shut-Down Systems should have:
1) Force guided relay enables a feedback path just in case of welded contacts and
eliminates the need for simplifies Proof Testing. (ESD-Emergency Shut Down and F&G-Fire & Gas systems)
Safety relays for F&G-Fire & Gas Systems should have:
The diagram below shows connection details for a safety relay used by Fire & Gas Systems. The Fire & Gas System is always on standby mode and it becomes more important to have multiple diagnostics to make sure the Fire and Gas System Safety Relay is still functional and all wirings are connected.
- Diagnostics for lost power input to field devices: Beacons, Solenoid Valves, Fire Alarm Bell.
- Field devices disconnection diagnostics.
- Short circuit field device diagnostics.
- Diagnostics for any welded contacts.
- Proof Test points (TP1, TP2, TP3) without the use of external power.
- All diagnostics via the same cable (A1,A2) by the use of test pulse filtering.
- Option for redundant connection (A1’, A2’).
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